#include <string>
class Accout {
public:
    void calculate() { amount += amount * interstRate; }
    static double rate() { return interstRate; }
    static void rate(double);
private:
    std::string owner;
    double amount;
    static double interstRate;
    static double initRate();
};

void Accout::rate(double d) {

}

double Accout::initRate() {
    return 10.0;
}

double Accout::interstRate = initRate();